The present invention relates to a driver device which causes a vibrator to produce driving vibrations, a physical quantity measuring device (e.g. vibrating gyroscope) using the driver device, an electronic instrument, and the like.
Gyroscopes are classified as a rotating gyroscope, a vibrating gyroscope, and the like depending on the method of detecting the force applied to an object. In particular, a vibrating gyroscope is considered to be advantageous for reducing size and cost from the viewpoint of the constituent elements and the like. As a vibrating gyrosensor which detects an angular velocity applied to an object, a piezoelectric vibrating gyrosensor is known which excites a crystal or a piezoelectric element that is advantageous for increasing reliability and reducing size. A piezoelectric vibrating gyrosensor utilizes a phenomenon in which a Coriolis force occurs perpendicularly to vibrations when an angular velocity is applied to a vibrating object.
For example, a vibrating gyrosensor which detects an angular velocity causes a physical quantity transducer (vibrator) to produce driving vibrations in a specific direction. When an angular velocity is applied to the vibrator, a Coriolis force occurs perpendicularly to driving vibrations to produce detection vibrations. Since the detection vibrations occur perpendicularly to the driving vibrations, a detection signal (signal component due to detection vibrations) differs in phase from a drive signal (signal component due to driving vibrations) by 90 degrees. The detection signal can be synchronously detected separately from the drive signal utilizing the above phenomenon, for example.
A vibrating gyrosensor is used in a wide variety of applications, such as shake detection for a video camera or a digital camera, positioning using the global positioning system (GPS) for a car navigation system, and aircraft or robot position detection.
A vibrating gyrosensor used in these applications is driven by a battery. Therefore, it is necessary to increase the life of the battery by reducing the power consumption of the vibrating gyrosensor as much as possible. In this case, it is preferable to stop supplying power to the vibrating gyrosensor when an angular velocity or the like is not detected and to supply power to the vibrating gyrosensor from the battery only when using the vibrating gyrosensor. This makes it necessary to cause the vibrating gyrosensor to perform a normal operation within a short period of time after activation.
JP-A-2004-286503 and JP-A-2003-240556 disclose technologies for reducing the startup time of the vibrating gyrosensor, for example. JP-A-2004-286503 discloses technology in which a CR oscillation circuit or a ring oscillator is provided in an oscillation loop so that the oscillation amplitude is increased by an amplifier immediately after activation. JP-A-2003-240556 discloses technology in which a resistor is provided in series with a crystal vibrator to reduce the period of time until a signal from the vibrator becomes stable.
A vibrating gyrosensor driver device must cause a vibrator to constantly vibrate (oscillate) at its resonance frequency in order to stably detect the angular velocity applied to the vibrator. The driver device also must cause the vibrator to oscillate and start a normal operation within a short time. Moreover, it is preferable to form the driver device using a small circuit with low power consumption in order to increase the life of a battery at low cost.
On the other hand, when forming the vibrator using a crystal with a high Q value and hermetically sealing the vibrator in a package, the driving Q value of the vibrator increases to a large extent. Therefore, the period of time (startup time) until a signal from the vibrator becomes stable increases when causing the vibrator to produce driving vibrations.
However, according to the technology disclosed in JP-A-2004-286503, when causing the crystal vibrator to oscillate at a frequency close to the driving frequency of the crystal vibrator, the areas of the capacitor and the resistor of the CR oscillation circuit must be increased. This results in an increase in size and cost of a vibrating gyroscope (vibrating gyrosensor). According to the technology disclosed in JP-A-2004-286503, it is difficult to cause the crystal vibrator with a high Q value to operate at its driving frequency because the crystal vibrator is driven at another frequency during startup. Therefore, the period of time until stable oscillations are achieved increases when affected by manufacturing variations and the like. According to the technology disclosed in JP-A-2004-286503, the vibrator is driven by a rectangular wave after oscillations have started. Therefore, energy is lost even in the steady oscillation state, whereby power consumption increases as compared with the case of driving the vibrator by a sine wave.
The technology disclosed in JP-A-2003-240556 requires that a resistor be inserted. In general, when incorporating a resistor in an integrated circuit device, it is difficult to provide a vibrator with desired energy due to a large manufacturing variation in the resistor. According to the technology disclosed in JP-A-2003-240556, the gain is reduced because the energy applied to the vibrator is divided by the resistor.